JD 750, loader and backhoe stopped working - scratching noise video

[nick26]

Hey Guys,
I am new here. I have a 86' John Deere 750 tractor with a #67 loader and a #7 backhoe. Last fall it was taking forever to warm up and the hydraulics were kind of jerky, so I replaced all the fluid, cleaned the screen (there was a lot of crap on it), and replaced the filter and refilled it with the green bucket Coastal Multitrac tractor fluid that you can get at autozone (I was told this was ok to use on this tractor by a local hydraulic shop, please let me know if not, and what to use instead). After that the hydraulics ran pretty smooth and I used it over the winter a few times and a couple times in the spring, but then the hydraulics started to get really jerky and sometimes I had to turn the steering wheel to just the right spot for them to work at all. Now they don't work at all (but steering does), I let it warm up but still nothing moves. Now it is making this awful scratching noise (it used to make this noise once in a while but never seemed to effect the operation) and the noise starts and stops depending which position the steering wheel is in. I am afraid the pump might be dead? Please take a look at this video and let me know what you think:MOV_1006_comp.mp4

Thanks for you help.

 

[nick26]

I forgot to mention I double checked fluid and it is right in the middle of the dipstick. I was considering cleaning the screen again (could there be there was a lot of crap in there just waiting to get caught again?) but wanted to check with you guys before I drained all the oil again.

 

[tman1020]

Well I'm no mechanic but the pump would be my first guess however cleaning the screen again doesn't sound like it would hurt to try. One thing for sure I won't be using any of that green pail fluid you're talking about.

 

[boggen]

not a clue about tractor, and i am no mechanic by no means.... but i am questioning if you have 2 pumps vs one.

double checking. power steering pump most likely next to alternator up by the fan blade on the engine. power steering pump could be on same or opposite side of alternator, and ran from same belt. (possibly cooling water pump for engine also ran from same belt)
double checking. hydraulic pump for FEL / backhoe. coming off the engine in the very front, of the engine. and not off the belt/pully that goes around they engine fan / alternator / power steering pump. the hyd pump for FEL / backhoe, maybe position behind the engine, possibly tied in some place before going into transmission.
double checking is there a filter by pass for hyd oil for FEL / backhoe? by pass may be partial built into filter / were it screws in at.

it is easier to goto Home | Messick's and get to john deere parts listings / diagrams. than it is to go through john deere website.

if ya half way mechanically inclined. might suggest a "shop manual / service manual" for your tractor. it should give full break down of testing / tearing things apart, and putting it all back together with better diagrams, than what you find in part diagrams.

 

[nick26]

One thing for sure I won't be using any of that green pail fluid you're talking about.

Ok, what should I use instead and where can I typically buy it?

 

[beenthere]

I'd look again at the screen. If a lot of metal filings on it, then it might help answer the scratching noise we hear on the video.

And I'd use the Deere fluid if me.

And jdparts.com is not difficult to use, per boggen's comment about a Deere website, but don't know what he has tried either.

 

[kebo]

I would suggest getting a hyd pressure gauge that you can attach to one of the fittings. I have one for my JD 790 that I can attach to one of the hoses for the loader. I got it from a local hydraulic shop for about $25 with the quick connect fitting. All I have to do is remove a loader hose, install the gauge, crank it up and run up the rpm's some, then work the SCV valve to see the gauge deflect and read the pressure. Not sure what yours is supposed to read, but on mine I think it is 2000 PSI factory, although I shimmed mine out to 2500 PSI.

I suspect you would see low pressure if you had a gauge on it, maybe it would even give you erratic readings because of the way it's behaving. I third using the JD fluid too. Good luck, hope you get it figured out.

 

[Billrog]

Check the screen if it's plugged up your starving the pump and that gets expensive. I've check screens on machines and never seen them anything but clean there should be no crud in a hydraulic system.

 

[tman1020]

Ok, what should I use instead and where can I typically buy it?

I'm not sure what john Deere recommends but I would start there. I use the premium fluid from TSC. I'm not certain but I believe the John Deere 750 is made by Yanmar and I have used the tsc brand tractor hydraulic fluid in similar size and year Yanmar tractors with no problem. Keep us posted.

 

[Mike68]

I just did a full fluid change on my 750. The JD shop recommended the JD Hygard Low Viscosity. I asked about the regular Hygard since the Low Vis upper limit temp range is 86F ambient.

Two different dealers told me the Low Viscosity was what I should use. I am in Connecticut.

I don't have power steering so I am not sure if there is a second pump. The JD parts website has great exploded diagrams.

When I cleaned my screen it collected some fine metal shavings about to size of a single pea. Other than that it was very clean. That was after 7 years and 150 hours since the last fluid change.